The German netted twice either side of half-time to become the Seagulls first-ever Premier League goalscorer and send them to their first top-flight victory in 34 years. The last was a 1-0 home success over Coventry City on April 22, 1983.
In netting, Gross also became their maiden top-flight goalscorer since Gordon Smith, who netted in a 2-1 defeat at Norwich on 14 May 1983.
Tomer Hemed also shrugged off his mid-week injury worries to notch a third as that man Gross turned provider.
It was achieved against a West Bromwich Albion side that went into the match in fine form, unbeaten and sitting fifth in the table.
A tough afternoon was expected for the home side, but a sterling showing saw them ahead to Gross' deflected goal just before half-time after they had stifled their visitors.
And the same man made it 2-0 moments into the second half in a game that saw John Motson, who announced he would be retiring at the end of the season earlier this week, covering his first-ever game at the Amex.
Hemed made the starting line, while Jose Izquierdo was only named on the bench along with Glenn Murray, who also quelled his injury fears. New signings Ezequiel Schelotto and Tim Krul were not even named in the Seagulls squad.
West Brom handed a debut to new signing Grzegorz Krychowiak, while Kieran Gibbs was named on the bench.
It was a chess-like start in the opening ten-minutes with both side cancelling each other out until the home side thought they had their first Premier League goal on 14 minutes.
A fierce Solly March effort from outside the box after a free kick was poorly dealt with by Ben Foster and the ball popped up to Shane Duffy to tap home, but the assistant referee correctly had his flag up for offside against the Irishman.
Anthony Knockaert then sent an effort straight at Foster, while at the other end, Albion old boy Gareth Barry had the first effort for the visitors which was blocked away and looked suspiciously like a corner, despite a goal kick being given.
The home side went on to dominate the majority of the rest of the half. With an increased tempo and controlling possession, Brighton got the ball into good areas out wide, but the only thing lacking was the final ball as they fully stifled their visitors.
That was until the 39th minute when Barry gave a stark reminder of West Brom's attacking threat as he was left in space on the edge of the box and lashed an effort at Mathew Ryan's goal, but the Australian acrobatically turned it behind.
Back at the other end, Knockaert laid into Pascal Gross, who had time and space to turn just outside the 18-yard box, but his left-footed shot curled just over the bar.
And Albion's endeavor was rewarded as they took the lead with their maiden Premier League goal on the stroke of half-time. March stood the ball up to the far post and Gross took it down, and, in all honesty looked like he had taken too much time, but managed to guide the ball into the bottom corner via a hefty deflection.
West Brom may have had a Tony Pulis rocket at them at half-time after an animated first-half from the manager on the touchline, but it was a Brighton rocket that started the second half.
The Seagulls doubled their lead within three minutes as Gross found space, looked up and let fly with a low effort from 22 yards that nestled into the bottom corner.
West Brom tried to shuffle their pack as Gibbs came on for his debut and Oliver Burke was also introduced, but it made little difference with the home side in control.
And it was 3-0 on 63 minutes as two-goal hero Gross turned provider as he crossed for Hemed to head home at the near post.
The visitors did give themselves a faint lifeline with 13 minutes left as substitute James Morrison fired home a first-time shot from Burke's header down across the box.
It set up a few nervy moments in the closing stages as the visitors enjoyed the majority of possession, but the closest they came was when Barry curled narrowly over with four minutes to go.
Brighton & Hove Albion: Ryan, Bruno, Duffy, Dunk, Suttner, Knockaert, Propper, Stephens, March, Gross, Hemed (Murray 83). Unused subs: Maenpaa, Rosenior, Huenemeier, Skalak, Murphy, Izquierdo.
West Brom: Foster, Nyom, Evans, Dawson, Hegazi (Gibbs 56), Livermore (Morrison 70), Barry, Phillips, Krychowiak, Rodriguez, Rondon (Burke 56). Unused subs: Myhill, Yacob, Brunt, McClean.
Referee: Chris Kavanagh.